For updating the Navigation, login to the portal with the user having Administrator web role.
Hover over the Navigation and select Edit
This opens up the dialog box, here we can edit or insert a new navigation link. To add new navigation link click on “+”
We can either specify any existing page within portal or can point to any external URL and can also show up image + text or image only.
This adds the new navigation link
Similarly, we can add new child links or move a link as child link which then appears as drop down. Here we have moved the new Search Home link inside Support by dragging.
The updated navigation looks like below
Hope it helps..